Hollow sphere structure of metal-containing tungsten carbide, method for manufacturing the same, method for manufacturing film

ABSTRACT

A hollow sphere structure of metal-containing tungsten carbide (WC-based cermet contains one or two metal elements to form a pseudo binary eutectic) is provided, which includes a porous shell of metal-containing metal carbide surrounding a hollow core. The hollow sphere structure has a diameter of 5 micrometers to 45 micrometers, and the porous shell has a thickness of 0.1 micrometers to 12 micrometers. The metal is cobalt, nickel, or a combination thereof

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Divisional of pending U.S. patent application Ser.No. 15/454,211, filed Mar. 9, 2017 and entitled “Hollow sphere structureof metal-containing tungsten carbide, method for manufacturing the same,method for manufacturing film”, which is based on, and claims priorityfrom, Taiwan Application Serial Number 105141021, filed on Dec. 12,2016, the disclosure of which is hereby incorporated by reference hereinin its entirety.

TECHNICAL FIELD

The technical field relates to a hollow sphere structure ofmetal-containing tungsten carbide, a method for manufacturing the same,and an application thereof.

BACKGROUND

Tungsten carbide exhibits abrasion resistance, and therefore is oftenused as a function material in cutting tools, spray guns, casting molds,and other abrasion-resistant components. An important topic in thedevelopment of modern tungsten carbide materials is how to enhance itsinherently abrasion resistant efficiency so that it can be furtherapplied in petrochemicals, steel, and other industries. The lifespan ofconventional micro-scale particles of tungsten carbide material is shortdue to the layered particles easily becoming delaminated during use.However, either nano-scale or sub-micro-scale tungsten carbide materialis less brittle at room temperature (which is equal to improvedtoughness), thus inner stress in the film of the tungsten carbide arealso decreased. Simultaneously, a film formed from either nano-scale orsub-micro-scale tungsten carbide particles is free of layeredstructures, and the film will not be delaminated during use, therebyincreasing the lifespan of the film. However, the nano-scale orsub-microscale tungsten carbide particles have poor flowability and lowcompacted density, and it is difficult to directly compact them to froma body of high density. The body should be sintered at high temperaturefor a long period to increase the density of the sintered product, butthe above sintering process may induce grain growth in the product. Assuch, the product will lose its nano-scale or sub-microscale grain inits inner structure.

Accordingly, a novel tungsten carbide material structure is called for.

SUMMARY

One embodiment of the disclosure provides a hollow sphere structure ofmetal-containing tungsten carbide, comprising: a porous shell ofmetal-containing tungsten carbide surrounding a hollow core, wherein thehollow sphere structure has a diameter of 5 micrometers to 45micrometers, the porous shell has a thickness of 0.1 micrometers to 12micrometers, and the metal is cobalt, nickel, or a combination thereof.

One embodiment of the disclosure provides a method of forming a hollowsphere structure of metal-containing tungsten carbide, comprising:wet-dispersing a plurality of metal-containing tungsten carbideparticles to form slurry; and spray drying the slurry to connect themetal-containing tungsten carbide particles for forming the hollowsphere structure of metal-containing tungsten carbide by a spray dryer,wherein the hollow sphere structure of metal-containing tungsten carbideincludes a porous shell of metal-containing tungsten carbide surroundinga hollow core, wherein the hollow sphere structure has a diameter of 5micrometers to 45 micrometers, the porous shell has a thickness of 0.1micrometers to 12 micrometers, and the metal is cobalt, nickel, or acombination thereof.

One embodiment of the disclosure provides a method for manufacturing afilm, comprising: thermal spraying a hollow sphere structure ofmetal-containing tungsten carbide to form a metal-containing tungstencarbide film on a substrate, wherein the hollow sphere structure ofmetal-containing tungsten carbide includes a porous shell ofmetal-containing tungsten carbide surrounding a hollow core, wherein thehollow sphere structure has a diameter of 5 micrometers to 45micrometers, the porous shell has a thickness of 0.1 micrometers to 12micrometers, and the metal is cobalt, nickel, or a combination thereof

A detailed description is given in the following embodiments withreference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be more fully understood by reading the subsequentdetailed description and examples with references made to theaccompanying drawings, wherein:

FIG. 1 shows a hollow sphere structure of metal-containing tungstencarbide in one embodiment;

FIGS. 2A and 2B show SEM photographs of tungsten carbide particles inone embodiment;

FIGS. 3A to 3D show SEM photographs of an agglomerated hollow spherestructure in one embodiment;

FIGS. 4A and 4B show SEM photographs of a sintered hollow spherestructure in one embodiment;

FIG. 5 shows XRD spectra of the initial tungsten carbide particles andthe agglomerated hollow sphere structure in one embodiment;

FIGS. 6A to 6C show SEM photographs of a film formed by thermal sprayingthe hollow sphere structure in one embodiment;

FIGS. 7A and 7B show SEM photographs of a sintered hollow spherestructure in one embodiment;

FIGS. 8A and 8B show SEM photographs of a sintered hollow spherestructure in one embodiment;

FIGS. 9A and 9B show SEM photographs of a sintered hollow spherestructure in one embodiment;

FIGS. 10A to 10D show SEM photographs of commercially availablecobalt-containing tungsten carbide particles #1 in one embodiment;

FIGS. 11A to 11D show SEM photographs of commercially availablecobalt-containing tungsten carbide particles #2 in one embodiment;

FIG. 12A to 12C show SEM photographs of a film formed by thermalspraying the cobalt-containing tungsten carbide particles #1 in oneembodiment; and

FIG. 13A to 13C show SEM photographs of a film formed by thermalspraying the cobalt-containing tungsten carbide particles #2 in oneembodiment;

DETAILED DESCRIPTION

In the following detailed description, for purposes of explanation,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. It will be apparent,however, that one or more embodiments may be practiced without thesespecific details. In other instances, well-known structures and devicesare shown schematically in order to simplify the drawing.

One embodiment of the disclosure provides a method of forming a hollowsphere structure of metal-containing tungsten carbide. Metal is formedon tungsten carbide particles to obtain metal-containing tungstencarbide particles. The metal can be cobalt, nickel, or a combinationthereof. In one embodiment, the metal and the tungsten carbide of themetal-containing tungsten carbide particles have a weight ratio of 10:90to 14:86 (e.g. 12:88).

In one embodiment, the metal-containing tungsten carbide particlesbefore a process (e.g. ball-milling) have an original diameter of 0.2micrometers to 0.8 micrometers. The metal-containing tungsten carbideparticles after the process (e.g. ball-milling) have an originaldiameter of 0.05 micrometers to 0.6 micrometers. Processedmetal-containing tungsten carbide particles that are too small may causean agglomerated hollow sphere structure (formed in subsequent steps) tobreak easily during sintering. Processed metal-containing tungstencarbide particles that are too big cannot be agglomerated to form thehollow sphere structure. In one embodiment, the processedmetal-containing tungsten carbide particles include two grades: Grade Iparticles and Grade II particles have different diameters. For example,Grade I particles have a diameter of 0.05 micrometers to 0.2micrometers, and Grade II particles have a diameter of 0.2 micrometersto 0.6 micrometers. Compared to the hollow sphere structure formed ofthe metal-containing tungsten carbide particles with a single diameter(e.g. only Grade I particles or Grade II particles), the hollow spherestructure formed of the combination of Grade I particles and Grade IIparticles is less easy to result in the bursting of agglomeratedparticles after consequent sintering process. In one embodiment, Grade Iparticles and Grade II particles have a weight ratio of 0.08:1 to 100:1.In conventional art, it is difficult to directly aggregate Grade I (orGrade II) primary nano-scaled (or submicron-scaled) particles to formmicro-scaled secondary particles. Too high a ratio of Grade II particles(or Grade II particles) will be similar to the effect of utilizing theparticles of a single diameter.

Subsequently, the metal-containing tungsten carbide particles arewet-dispersed to form slurry. In one embodiment, 1 part by weight of themetal-containing tungsten carbide particles, 0.007 to 0.1 parts byweight of the polyvinyl alcohol (PVA), 0.5 to 5 parts by weight ofwater, and 1 to 10 parts by weight of alumina or zirconia mill balls(having a diameter of 4mm to 12mm) are put into a ball-milling machineto be wet ball-milled at 200 rpm to 500 rpm for 1 hour to 4 hours,thereby obtaining slurry.

The slurry is fed into a spray drier (YS-SD-2, commercially availablefrom Inora) at a feeding rate of 10 rpm to 20 rpm, and then stirred inthe spray dryer at 150 rpm to 200 rpm. The slurry was then sprayedthrough a nozzle at a pressure of 0.1 bar to 1 bar, and then dried withhot air of 150° C. to 200° C. for agglomeration. The pressure differenceof the nozzle was between −10Pa to −20Pa, and the air hammer frequencywas 1 to 3 Hz. After the spray drying, the metal-containing tungstencarbide particles 11 will be connected to form the hollow spherestructure 10, as shown in FIG. 1. The hollow sphere structure 10 of themetal-containing tungsten carbide includes a porous shell 13 surroundinga hollow core 15. The hollow sphere structure has a diameter of 5micrometers to 45 micrometers, and its porous shell has a thickness of0.1 micrometers to 12 micrometers. Too thin a shell 13 will bedelaminated and spread. Too thick a shell 13 will form a solid corestructure. In one embodiment, the porous shell 13 includes a pluralityof pores with a diameter of 0.3 micrometers to 2 micrometers. Pores thatare too small may cause the hollow sphere structure break easily duringsintering. It is difficult to form a hollow sphere structure with poresthat are too big.

In one embodiment, the hollow sphere structure can be directly thermalsprayed to form a metal-containing tungsten carbide film on a substrate.For example, the hollow sphere structure of cobalt-containing tungstencarbide can be thermal sprayed by a mixture gas of propane, oxygen, andnitrogen to form the cobalt-containing tungsten carbide film on thesubstrate. In one embodiment, the propane pressure is 3 bar to 10 bar,the oxygen pressure is 2 bar to 10 bar, and the nitrogen pressure is 1bar to 10 bar. Compared to thermal spraying a solid core ofmetal-containing tungsten carbide, thermal spraying the hollow spherestructure of metal-containing tungsten carbide may form a denser filmwith fewer pores and smaller tungsten carbide particles.

Alternatively, the hollow sphere structure of metal-containing tungstencarbide can be optionally sintered to form an irregular worm-shapedstructure or a multi-edge angle structure on an inner surface and anouter surface of the porous shell. In one embodiment, the sinteringprocess is performed at a temperature of 1000° C. to 1200° C. under anatmosphere of nitrogen for a period of 10 minutes to 30 minutes. In oneembodiment, the irregular worm-shaped structure has a length×width ofabout 0.3 micrometers×1.7 micrometers to 0.3 micrometers×0.7micrometers, and the multi-edge angle structure has a length×width ofabout 0.3 micrometers×2.6 micrometers to 0.5 micrometers×1.8micrometers. In addition, the connected metal-containing tungstencarbide particles in the porous shell have a strip-shaped nanostructurewith a length×width of about 130nm to 500 nm×13nm to 44nm. Themetal-containing tungsten carbide particles can be further connected bythe sintering step, thereby avoiding the particles becoming delaminatedfrom the hollow sphere structure.

Below, exemplary embodiments will be described in detail with referenceto accompanying drawings so as to be easily realized by a person havingordinary knowledge in the art. The inventive concept may be embodied invarious forms without being limited to the exemplary embodiments setforth herein. Descriptions of well-known parts are omitted for clarity,and like reference numerals refer to like elements throughout.

EXAMPLES Example 1

First, tungsten carbide particles (Kallex) with a diameter of 0.8micrometers were provided. The SEM photographs of the tungsten carbideparticles are shown in FIGS. 2A and 2B. In FIG. 2B, the tungsten carbideparticles in region A had irregular shapes, and the tungsten carbideparticles in region B had slightly regular cleaved crystal facestructures. Subsequently, cobalt was formed on the tungsten carbideparticles. 1 part by weight of the cobalt-containing tungsten carbide,0.02 parts by weight of polyvinyl alcohol (PVA), 1.5 parts by weight ofwater, 3.3 parts by weight of alumina mill balls (having a diameter of8mm) were then mixed and put into a ball-milling machine to be wetball-milled at 327 rpm for 4 hours, thereby obtaining slurry. After theprocess and treatment (e.g. ball milling), the cobalt-containingtungsten carbide particles in the slurry had a diameter of 0.05micrometers to 0.6 micrometers.

The slurry was fed into a spray dryer (YS-SD-2, commercially availablefrom Inora) at a feeding rate of 20 rpm, and the slurry stirred at 150rpm during the spray drying process. The slurry was then sprayed througha nozzle at a pressure of 1 bar, and then dried with hot air of 150° C.to 200° C. to vaporize the moisture thereof, thereby forming a group ofagglomerated particles. The pressure difference of the nozzle wasbetween −10Pa to −20Pa, and the air hammer frequency was 1 to 3 Hz. Thegroup of agglomerated particles was a hollow sphere structure, and SEMphotographs thereof are shown in FIGS. 3A to 3C. An SEM photograph of across-section of the hollow sphere structure is shown in FIG. 3D, and ashell of the hollow sphere structure had a thickness of about 11.5micrometers. The hollow sphere structure had a porous shell surroundinga hollow core, and the porous shell was composed of a plurality ofconnected cobalt-containing tungsten carbide particles. The hollowsphere structure was analyzed by energy dispersive X-ray spectrometry(EDS) to determine its elements: C (13.8 wt %), Co (13.13 wt %), and W(73.07 wt %).

The hollow sphere structure was put under a low pressure environment(1×10⁻² ton to 3×10⁻² torr), and nitrogen with a flow rate of 10liters/minute to 30 liters/minute was then introduced into theenvironment. The hollow sphere structure was then heated to and sinteredat 1000° C. for 10 minutes. SEM photographs of the sintered hollowsphere structure are shown in FIGS. 4A and 4B, in which the innersurface and the outer surface of the porous shell had an irregularworm-shaped structure (Region A, having a length of about 0.3micrometers to 2 micrometers) and a multi-edge angle structure (RegionB, having a length of about 0.8 micrometers to 2 micrometers). Inaddition, the connected cobalt-containing tungsten carbide particles inthe porous shell had strip-shaped nanostructures (Regions C and D). Thenanostructure in region C had a length×width of about 131nm×12.5nm, andthe nanostructure in region D had a length×width of about 500nm×43.7nm.FIG. 5 shows XRD spectra of the initial tungsten carbide particles(without pure cobalt phase formed thereon) (PDF#73-0471) and theagglomerated hollow sphere structure, and it determined that the majorphase of the hollow sphere structure was tungsten carbide crystal phasewithout pure cobalt phase or without other decomposition phases, e.g.,Co₃W₃C, Co₆W₆C, Co₇W₆, W₂C, W, graphite, or diamond phase, or withoutother oxide phases, e.g., WO₃, WO₂, CoO, Co₃O₄ CoO₂, CO phase. This XRDevidence for the agglomerated hollow sphere structure tungsten carbideparticles presents that WC and Co form a pseudo binary eutectic (α-WC,hcp (hexagonal close packed)) in the W—C—Co system.

Subsequently, the hollow sphere structure was thermal sprayed by amixture gas of 5.2bar of propane, 8 bar of oxygen, and 5 bar of nitrogento form a cobalt-containing tungsten carbide film with a thickness of100 micrometers on a substrate. The thermal spray equipment was CDSR-75C (commercially available from Struers), the feed rate was 17 rpm,the feed inlet and the substrate had a distance of 203mm therebetween,and the a movement rate of nozzle was 1200 mm/second. FIGS. 6A to 6Cshow SEM photographs of a cross-section of the film. As shown in FIG.6A, the film had very few pores. As shown in FIG. 6C, most of thetungsten carbide particles (long-shaped particles) in the film wereround-angled particles, which were suitable for used in knives (due tolowering the cleave possibility caused from stress concentration). Thefilm was quantitatively analyzed by EDS to determine its content: C(5.54 wt %), O (0.84 wt %), Co (10.95 wt %), and W (82.67 wt %), whichwas close to the ideal atomic ratios (e.g. C (5.5 wt %), Co (11 wt %),and W (83.5 wt %)).

Example 2

Example 2 was similar to Example 1, with the difference being that theinitial tungsten carbide particles had a diameter of 0.2 micrometers.The other processing conditions of forming the cobalt on the tungstencarbide particles, agglomerating the particles to form the hollow spherestructure, and sintering the hollow sphere structure were similar tothose in Example 1, and the related descriptions are omitted here. FIGS.7A and 7B show SEM photographs of the sintered hollow sphere structure,in which the hollow sphere structure was partially broken after thesintering process.

Example 3

Example 3 was similar to Example 1, with the difference being that theinitial tungsten carbide particles included 25 wt % of particles with adiameter of 0.2 micrometers and 75 wt % of particles with a diameter of0.8 micrometers. The other processing conditions of forming the cobalton the tungsten carbide particles, agglomerating the particles to formthe hollow sphere structure, and sintering the hollow sphere structurewere similar to those in Example 1, and the related descriptions areomitted here. FIGS. 8A and 8B show SEM photographs of the sinteredhollow sphere structure, in which more pores were formed in the shell ofthe hollow sphere structure, such that the hollow sphere structure wasnot broken after the sintering process.

Example 4

Example 4 was similar to Example 1, with the difference being that theinitial tungsten carbide particles included 50 wt % of particles with adiameter of 0.2 micrometers and 50 wt % of particles with a diameter of0.8 micrometers. The other processing conditions of forming the cobalton the tungsten carbide particles, agglomerating the particles to formthe hollow sphere structure, and sintering the hollow sphere structurewere similar to those in Example 1, and the related descriptions areomitted here. FIGS. 9A and 9B show SEM photographs of the sinteredhollow sphere structure, in which more pores were formed in the shell ofthe hollow sphere structure, such that the hollow sphere structure wasnot broken after the sintering process.

Comparative Example 1

Sources, cobalt content, and particle diameter of several commerciallyavailable cobalt-containing tungsten carbide particles are tabulated inTable 1.

TABLE 1 Cobalt Particle content diameter No. Manufacture (%) (μm) 1Sulzer Metco 12 15-45 2 NEI 12 <44

FIGS. 10A to 10B show SEM photographs of cobalt-containing tungstencarbide particles # 1, and FIG. 10D shows an SEM photograph of across-section of the cobalt-containing tungsten carbide particles # 1(Solid core structure). The cobalt-containing tungsten carbide particles# 1 were thermal sprayed by a mixture gas of 5.2 bar of propane, 8 barof oxygen, and 5 bar of nitrogen to form a cobalt-containing tungstencarbide film with a thickness of 100 micrometers on a substrate. Thethermal spray equipment and conditions were similar to those in Example1, and the related descriptions are omitted here. FIGS. 12A to 12C showSEM photographs of a cross-section of the film. As shown in FIG. 12A,the film had obvious pores. As shown in FIG. 12C, the tungsten carbideparticles in the film had the shape of an eggshell fracture and adiameter of 367 nm to 1067 nm. In other words, the film had a crackedgrain of tungsten carbide.

The cobalt-containing tungsten carbide particles # 2 were thermalsprayed by a mixture gas of 5.2 bar of propane, 8 bar of oxygen, and 5bar of nitrogen to form a cobalt-containing tungsten carbide film with athickness of 100 micrometers on a substrate. The thermal spray equipmentand conditions were similar to those in Example 1, and the relateddescriptions are omitted here. FIGS. 13A to 13C show SEM photographs ofa cross-section of the film. The film had many pores and cracks. Asshown in FIG. 13C, the film had many brighter large grains of tungstencarbide with a diameter of 267 nm to 2000 nm. The grains also had moresharp angles. Therefore, the film had more cracks.

It will be apparent to those skilled in the art that variousmodifications and variations can be made to the disclosed methods andmaterials. It is intended that the specification and examples beconsidered as exemplary only, with the true scope of the disclosurebeing indicated by the following claims and their equivalents.

What is claimed is:
 1. A method of forming a hollow sphere structure ofmetal-containing tungsten carbide, comprising: wet-dispersing aplurality of metal-containing tungsten carbide particles to form slurry;and spray drying the slurry to connect the metal-containing tungstencarbide particles for forming the hollow sphere structure ofmetal-containing tungsten carbide without pure cobalt phase, otherdecomposition phases, or other oxide phases, wherein the hollow spherestructure of metal-containing tungsten carbide includes a porous shellof metal-containing tungsten carbide surrounding a hollow core, whereinthe hollow sphere structure has a diameter of 5 micrometers to 45micrometers, the porous shell has a thickness of 0.1 micrometers to 12micrometers, and the metal is cobalt, nickel, or a combination thereof,wherein the other decomposition phases include Co₃W₃C, Co₆W₆C, Co₇W₆,W₂C, W, graphite, or diamond phase, and wherein the other oxide phasesinclude WO₃, WO₂, CoO, Co₃O₄ CoO₂, or CO phase.
 2. The method as claimedin claim 1, wherein the porous shell has a plurality of pores, and thepores have a diameter of 0.3 micrometers to 2 micrometers.
 3. The methodas claimed in claim 1, wherein the metal-containing tungsten carbideparticles have a metal formed on tungsten carbide particles.
 4. Themethod as claimed in claim 1, wherein the metal-containing tungstencarbide particles have a diameter of 0.05 micrometers to 0.6 micrometersin the slurry.
 5. The method as claimed in claim 1, wherein themetal-containing tungsten carbide particles after spray drying includetwo grades, wherein Grade I particles have a diameter of 0.05micrometers to 0.2 micrometers, Grade II particles have a diameter of0.2 micrometers to 0.6 micrometers, and Grade I particles and Grade IIparticles have different diameters.
 6. The method as claimed in claim 5,wherein Grade I particles and Grade II particles have a weight ratio of0.08 to
 1. 7. The method as claimed in claim 1, wherein the metal andthe tungsten carbide particles of the metal-containing tungsten carbideparticles have a weight ratio of 10:90 to 14:86.
 8. The method asclaimed in claim 1, further sintering the hollow sphere structure ofmetal-containing tungsten carbide to form an irregular shaped structureor a multi-edge angle structure at an inner surface or an outer surfaceof the porous shell.
 9. A method for manufacturing a film, comprising:thermal spraying a hollow sphere structure of metal-containing tungstencarbide to form a metal-containing tungsten carbide film on a substrate,wherein the hollow sphere structure of metal-containing tungsten carbideincludes a porous shell of metal-containing tungsten carbide surroundinga hollow core, wherein the hollow sphere structure has a diameter of 5micrometers to 45 micrometers, the porous shell has a thickness of 0.1micrometers to 12 micrometers, and the metal is cobalt, nickel, or acombination thereof.